1. Field of the Invention
The present invention relates to clays having sorptive properties. Such clays are known collectively as fuller's earth and are characterized by the fact that they absorb water, oils and greases and are capable of removing undesirable constituents, such as dyes and coloring matter from aqueous solutions and from oils. Included in this group of clays are attapulgite, sepiolite, and bentonites.
2. Prior Art
Attapulgus clay, hereinafter referred to as attapulgite, has a wide variety of commercial uses deriving from its high surface area, sorptivity and decolorizing power. For many uses a comparatively hard granular material of high sorptive power is required which will not disintegrate on contact with water. Important uses of this type are materials used to absorb water and mixtures of oil and water from floors, materials used for animal bedding, commonly called pet litter and materials used as carriers for agricultural products. In many cases it is also desirable that the material should exhibit a substantially neutral pH in water.
Natural Attapulgus clay does not have sufficient sorptive properties or sufficient hardness for commercially practicable purposes and it is customary to apply various degrees of thermal activation to the clay in order to develop the required properties depending upon the purpose for which the product is to be used. The effect of thermal activation on Attapulgus clay is described in an article by W. S. W. McCarter, et al "Thermal Activation of Attapulgus Clay", Industrial & Engineering Chemistry, Vol. 42, No. 3 March 1950, pages 529 to 533. Sorptive properties and hardness adequate for some applications are obtained by heating the clay to a temperature of 400.degree. to 500.degree. F.; the product of this thermal activation retains much of the water of constitution, typically 15 to 18% as measured by volatile matter at 1200.degree. F. However, such activated clays have little resistance to disintegration by contact with water which converts them to a sludge of fine particles. Such materials are not, therefore, practicable for many applications, such as floor absorbents and pet litter. In order to confer the necessary resistance to water, the clay must be activated at a higher temperature, typically 800.degree. to 1000.degree. F. which results in loss of most of the water of constitution, the product containing 5% or less of volatile matter at 1200.degree. F. Although clays activated at these higher temperatures have the required sorptivity, hardness and resistance to water they are more costly to produce, particularly because of the greater energy requirements to raise the temperature and to drive off the water of constitution.
It is an objective of the present invention, therefore to provide a process for producing a sorptive clay of acceptable hardness and resistance to water disintegration without the need for the more extensive thermal activation heretofore required. It is a further objective of the invention to provide such a process wherein the product exhibits a substantially neutral pH in water.